1. Field of the Invention
The field of the invention relates to methods of modulating at least one trait in a plant. Such traits include increased or decreased time to flowering and other traits associated with the shade avoidance syndrome. Also encompassed are transgenic plants produced by the disclosed methods.
2. Description of the Related Art
The influence of light on plant growth and development has been a topic of interest from the earliest studies of plant physiology. Flowering plants are subject to photoperiodism which is generally defined as the response of plants and animals to relative lengths of day and night. Plants are also sensitively attuned to differences in light quality. Red light, Far red light and blue light receptors are well characterized across plant species. One aspect of plant physiology that is particularly affected by photoperiodism and light quality is flowering.
The transition to flowering in plants is regulated by environmental factors such as temperature and light. In Arabidopsis thaliana, much is known about the photoperiod pathway that induces flowering in response to an increase in daylength. In contrast, the mechanisms that regulate flowering in response to changes in light quality are largely unknown. In crowded or shaded environments, the red/far-red ratio of incoming light reaching plants decreases, and a series of responses known collectively as the “shade avoidance syndrome” are triggered, including the promotion of stem elongation and acceleration of flowering (Ballare, C. L. Trends Plant Sci 4, 201, 1999; and Halliday, K. J., et al. Plant Physiol 104, 1311-1315, 1994). Phytochromes are a family of red/far-red-light photoreceptors essential for the perception of changes in light quality and shade avoidance responses; among the 5 phytochromes in Arabidopsis, a phytochrome B (phyB) plays the most significant role in the shade avoidance syndrome. The mechanisms by which phyB regulates flowering are largely unknown.
The phytochromes and the blue/UV-A photoreceptors called cryptochromes (cry1 and cry2 in Arabidopsis) are the most critical photoreceptors that regulate floral induction (Lin, C. Plant Physiol 123, 39-50, 2000). Several components involved in phytochrome signaling in seedlings have been isolated and characterized in recent years (Quail, P. H. Nat Rev Mol Cell Biol 3, 85-93, 2002). Seedlings defective in phytochrome A (phyA) signaling are tall under far-red light (FR) while plants defective in phyB signaling are tall under red-light (R). Despite the large number of components identified, it remains unclear how they are assembled into a signaling network. ELF3 and GI have been reported to have a role in flowering (Liu, X. L., et al. Plant Cell 13, 1293-304, 2001), mainly through mis-regulation of the circadian clock (Suarez-Lopez, P., et al. Nature 410, 116-20, 2001), but the mechanisms by which phytochromes regulate flowering directly are largely unknown. Using a new genetic screen for seedlings showing an enhanced response to R light and flowering time defects, a new recessive mutant, pft1 (phytochrome and flowering time 1) was isolated; the PFT1 locus was cloned and characterized in detail. PFT1 (PHYTOCHROME AND FLOWERING TIME 1) is a nuclear protein that plays an essential role in regulation of flowering time by phyB, acting downstream the photoreceptor to regulate the expression of the floral induction gene, FLOWERING LOCUS T (FT). As used herein, upper case refers to the wild type form of PFT1 and lower case refers to the mutant form.